A pink light alerting train passengers to give up their seats for pregnant travellers is being trialled in a South Korean city.

500 women in the country’s second-largest city, Busan, participate in the trial over five days on the Busan-Gimhae Light Rail service.

The pregnant women carried sensors that activate pink lights over priority seats when they board a train. The sensors have a battery life of six months, work via bluetooth and must be carried outside of their bag and clothing.

The Pink Light project is a collaboration between the city government and local businesses.

“Consideration for pregnant women should prevail and they should be able to use public transportation more easily and conveniently with this policy,” said Suh Byung-soo, Mayor of Busan. “Women should be able to use city facilities easily even when they are expecting,” he added.

Passengers can find it hard to tell whether a woman is pregnant and don’t want to offend those who are not. At the same time, commuters may be busy on their phones and do not always offer their seats to others.

In Singapore, pregnant women can ask station staff for “care stickers”, meant to let fellow-passengers know that they need a seat.

Busan plans to expand the pink lights to more train lines and buses, reports The Asahi Shimbun.

South Korea is trying to make travel more comfortable for expectant mothers, as it encourages people to have more children. South Korean women had 1.24 children on average in 2015, below the OECD average of 1.7.